Issue with smooth shading
A possible approach to do it with quads only :


Start with a square and subdivide it W then subdivide
Extrude E and scale down S
Make a copy and round it to sphere (Alt+Shift+S then move the mouse to the right)
Keep only the wanted vertices it each
Move back the angular part and align it : set the cursor as pivot point, select the vertices then scale S+Z0 and for the other part S+X0
Remove doubles




Concerning the shading, that may be dependent on your target system (sL ?)... so you may need to give it a try.

Possibilities :


Global smooth
Inner edge loop smooth
Global smooth + edgesplit modifier